1. Field of the Invention
This invention relates to a method of forming fine patterns in the field of photolithographic technology. More particularly, the invention relates to a method of forming or defining fine patterns, such as hole patterns and trench patterns, that can meet today's requirements for higher packing densities and smaller sizes of semiconductor devices.
2. Description of the Related Art
In the manufacture of electronic components such as semiconductor devices and liquid-crystal devices, there is employed the photolithographic technology which, in order to perform a treatment such as etching on the substrate, first forms a film (photoresist layer) over the substrate using a so-called radiation-sensitive photoresist which is sensitive to activating radiations, then performs exposure of the film by selective illumination with an activating radiation, performs development to dissolve away the photoresist layer selectively to form an image pattern (photoresist pattern), and forms a variety of patterns including contact providing patterns such as a hole pattern and a trench pattern using the photoresist pattern as a protective layer (mask pattern).
With the recent increase in the need for higher packing densities and smaller sizes of semiconductor devices, there is a growing demand for still finer patterns. Following the current tendency, use is made of short-wavelength radiations such as KrF, ArF and F2 excimer laser beams and electron beams (EB) as the activating light necessary in the formation of mask patterns. Further, active R&D efforts are being made to find photoresist materials as mask pattern formers that have physical properties adapted to those short-wavelength radiations.
In recent years, particular attempts have been vigorously made to develop ultrafine processing techniques with the use of high-energy light rays having wavelength of 200 nm or shorter (for example, ArF or F2 excimer laser beams) or electron beams and it is an important problem to be solved to form finer and more precise photoresist patterns using such photoresist materials adapted to ultrashort-wavelength radiations.
Existing pattern formation methods with the use of these photoresist materials adapted to ultrashort-wavelength radiations are typified by a method which comprises coating such a photoresist composition adapted to ultrashort-wavelength radiations on a silicon wafer, drying to form a photoresist layer, irradiating the photoresist layer selectively with high energy light rays having wavelength of 200 nm or shorter or electron beams, and then developing with an alkaline developer to thereby form patterns.
By the existing method as described above, however, it is very difficult to form fine patterns having pattern width or diameter of 100 nm or less. Even though such fine patterns as having pattern width or diameter of 100 nm or less can be formed, the obtained fine patterns frequently suffer from variations in the pattern dimensions and thus have troubles in uniformity (in-plane uniformity), etc. Accordingly, these patterns are unsuitable in practice for the production of semiconductors in most cases.
JP 2001-281886A discloses a method comprising the steps of covering a surface of a resist pattern with an acidic film made of a resist pattern size reducing material containing a water-soluble resin, rendering the surface layer of the resist pattern alkali-soluble, then removing said surface layer and the acidic film with an alkaline solution to reduce the feature size of the resist pattern. JP-2002-184673A discloses a method comprising the steps of forming a resist pattern on a substrate, then forming a film containing a water-soluble film forming component on said resist pattern, heat treating said resist pattern and film, and immersing the assembly in an aqueous solution of tetramethylammonium hydroxide, thereby forming a fine-line resist pattern without involving a dry etching step. However, both methods are simply directed to reducing the size of resist trace patterns themselves and therefore are totally different from the present invention in object.